The present invention relates to storage facilities for highly chilled liquified gases. More particularly, this invention relates to tethered submarine pressure transfer storage facilities for materials such as liquified natural gas (LNG).
It has been long known to liquify gases, including natural gas (methane), to reduce volume thereof and thereby facilitate transportation and storage. A significant drawback stemming from the liquifaction process is the vastly increased concentration of energy producing material with resultant substantial dangers and hazards to the immediate environment of such liquified materials.
Natural gas is a mixture of hydrocarbons, typically 65 to 90 percent methane, with smaller amounts of ethane, propane and butane. When natural gas is chilled to the below minus 263 degrees Fahrenheit, it becomes an odorless, colorless liquid having a volume which is less than one six hundredth (1/600) of its volume at ambient atmospheric surface temperature and pressure. When LNG is warmed above its -263 degrees Fahrenheit boiling point, it regassifies and expands to its ambient volume.
Of the known liquid energy gases, LNG is the most difficult to handle because it is so intensely cold relative to the general environment at sea level. Complex handling, shipping and storage facilities and procedures are required to prevent unwanted thermal rise in the stored LNG and resultant regassification.
The Pognowski U.S. Pat. No. 3,643,447 teaches a tethered flexible storage container for storing crude oil and the like in the ocean beneath an offshore drilling platform. It was intended to store petroleum materials at ambient seawater, and therefore does not relate to storage of highly chilled materials such as LNG. On the other hand, the Glazier U.S. Pat. No. 3,727,418 describes an insulated spherical storage vessel for LNG materials under water. Pressure transfer is not suggested in the Glazier patent, although a flexible membrane and a balancing fluid of 2-methyl butane (ethyldimethylmethane) are disclosed.
It is known in the art that the addition of pressure to stored LNG raises the boiling point and helps to promote liquid state thereof. The assignee of the present invention is the owner of the Cook and Stolowitz U.S. Pat. No. 4,232,983 which teaches the use of a submerged pressure transfer storage facility for LNG. The assignee of the present invention is the owner of two pending patent applications by Cook, Ser. No. 170,800 filed July 21, 1980, now U.S. Pat. No. 4,365,576, and Ser. No. 180,607 filed Aug. 25, 1980, now U.S. Pat. No. 4,402,632. Each of these references teaches various facets of deep seawater pressure transfer to stored LNG to promote and maintain liquid state. The present invention overcomes several significant difficulties encountered with these prior references and constitutes an improvement on the technology thereof.
One drawback of the prior art submarine pressure transfer storage facilities described above was the direct contact of seawater and marine life to the seal providing surfaces of those two part pressure transfer vehicles. Another drawback was the depth required to provide sufficient pressure transfer to promote liquid state of the LNG material stored therein (about 600 or more feet of water depth). Another drawback was the complex ballasting equipment needed for operating those facilities. One more drawback was the direct contact of seawater at the seal-providing region of the tank and the problem of preventing formation of ice at the seal, thereby impeding the pressure transfer function.